In today's computer networks, sharing data among devices has become desirable if not essential. Not only does the shared data need to be replicated on each device, but the set of replicated data must be synchronized so that changes made to one replica are reflected in all the others. Synchronization enables many users to work with their own local copy of shared data but have the shared data updated as if they were working on a single, centralized database. For shared data applications where users are geographically widely distributed, replication and synchronization are often the most efficient methods for effectively utilizing shared data.
In addition to desktop computers, workstations, and servers, modern computing environments often include lightweight handheld computing devices that fit into a pocket, purse, or day planner. Modern computing environments range from private networks to the Internet. Although a wide range of application programs can be executed on handheld computers, shared data applications are particularly popular and well suited for these devices. Shared data applications include, among many others, electronic calendars and task lists, electronic mail organizers, and electronic address books. A device running one or more of these applications stores electronic data that is or can be replicated and shared with other devices. It is desirable, if not essential, then to at least periodically synchronize data stored on each device. For example, many calendaring applications allow devices to share data or records concerning each user's appointments. It is important that when a new appointment is added or an existing appointment is modified on one device that addition or change is reflected on all devices providing calendaring.
Where the shared data applications on each device use the same data formats, synchronization is a relatively simple process. However, modern computing environments tend to be more complex, often having devices from multiple manufacturers, each with differing data formats making it difficult to accurately synchronize shared data. For example, where the data for one appointment is stored in one format on one device and in a second format on the other, synchronization sometimes results in the duplication of the appointment on each device.